1. Field of the Invention
In mining minerals and coal in underground tunnels, it is necessary to insure that there is no subsidence over the area until it has been mined so as to permit safe and effective mining of the area. There has, therefore, been a number of different ways to provide support for the over-burden to allow for substantial removal of the material being mined. Frequently, support has been obtained by leaving a significant portion of the mined material as a support means, in addition to having timbers and steel to provide additional support.
The above techniques are both inefficient and expensive. The mineral which is used for support is lost to recovery. The lumber and steel required is of relatively high cost and requires substantial labor to be installed initially and then is only partially recovered for reuse. It is therefore desirable to find new techniques which would allow for efficient removal of more of the material being mined and minimize the use of costly supporting materials.
2. Brief Description of the Prior Art
A technique referred to as the British Packwall concept is taught, where a wide drift is initially formed and a packwall introduced in the middle of the drift to provide support. In this concept, a relatively wide drift (such as 20-30 feet) is driven into a seam and provided with the necessary steel and/or wood roof and side supports. Forms for a concrete wall are then placed in the middle of the drift and filled with concrete. After hardening of the concrete, the forms for the wall and related drift roof supports are removed, with the concrete wall now forming the necessary support. British Pat. No. 1,043,687 teaches a method of mining coal in steep measures involving an upper and lower road, forming a plurality of steep drifts from the upper to the lower road, providing for load supporting concrete pillars to occupy the drifts, and then mining the mineral standing between the pillars. U.S. Pat. No. 3,892,442 teaches the use of a foam to fill mine cavities, to control roof fall and earth subsidence.